[PATCH] dix: report XI1 axis values correctly if first_valuator != 0

[Thomas Jaeger]

Peter Hutterer wrote:
> On Tue, Sep 22, 2009 at 09:12:01PM -0400, Thomas Jaeger wrote:
>> This raises an interesting question, though:  How are applications
>> supposed to keep track of the valuators they're interested in if events
>> only contain partial valuator information?  XI1 clients can select for
>> DeviceState and all Motion events to ensure they are always aware of the
>> valuator state, which seems a little wasteful but at least it'll work.
>> I see no way for XI2 clients to accomplish the same thing.
> 
> I hope I understand this correctly:
> The mask in each event specifies which valuators are set.
> - for relative axes, there's no "keeping track" anyway. So the first event
>   that has the matching valuator set matters.
This is fine.

> - for absolute axes, you get the initial state from the XIQueryDevice call
>   and then subsequent values through the events. if an event never contains
>   the valuator you need, it's value is unchanged from the original one.
This is the problematic case.  If the pointer is outside your
application's window, you won't get any motion events at all, so the
valuator might change without you knowing.  Event if the pointer stays
inside the application window all the time, you might not have selected
for all motion events, but only for ButtonMotion (XI1 or XI2 grabs) or
only for Press/Release events.